1. Field of the Invention
The present invention relates to a semiconductor device, such as an IC package, and a method of mounting this semiconductor device on a circuit board, and more particularly to a tape carrier package in which an IC chip is held on a film carrier, and also to a method of mounting this tape carrier package.
2. Prior Art
The conventional tape carrier package (hereafter referred to as a TCP for short) has a structure as follows.
FIG. 2 shows the structure of a conventional TCP, wherein FIG. 2(a) is a general perspective view of a TCP formed on a carrier tape, and FIG. 2(b) is a perspective view showing a TCP punched out from the tape carrier. FIG. 3 is a perspective view showing a method whereby a punched-out TCP is mounted on a circuit board.
As shown in FIG. 2(a), positioning holes 2, such as sprocket holes are formed in a tape 1. The tape 1 has a base film portion 4 with a device hole 3 formed therein. In the device hole 3, there is arranged an IC chip 5, which has a plurality of connection terminals provided therein.
The connection terminals of the IC chip 5 are connected to corresponding inner leads 6a, which extend from the base film into the device hole 3, and thus the IC chip 5 is held to the base film. Outer leads 6b extending beyond the base film portion 4 are at the outer ends opposite the inner leads 6a.
The inner leads 6a and the corresponding outer leads 6b are formed as one-piece bodies by patterning a metal foil.
The base film portion 4 is punched out from the tape 1 along with the leads 6b, which extend outward from the base film portion 4. Thus, a TCP 7 is formed as shown in FIG. 2(b). The TCP 7 has the IC chip 5 and the inner leads 6a covered with a resin material when necessary.
The TCP 7 punched out from the tape 1 is fixed to a circuit board 8 formed of a glass epoxy material or a glass material as shown in FIG. 3. To fix TCP 7 to the circuit board, the leads 6b of TCP 7 are located on bonding pads 9 of the circuit board 8.
Subsequently, the bonding pads 9 and the leads 6b, which have a bonding agent, such as solder or an anisotropic conductive film (not shown) placed therebetween, are subjected to thermocompression by a bonding tool 10, whereby the mounting of TCP 7 to the circuit board 8 is completed.
In the mounting method using the above-mentioned bonding tool 10, however, various types of bonding tools 10 need to be prepared, so that the best suited type can be selected according to the size and the shape of a TCP 7 to be mounted.
It is also required to reciprocate a bonding tool 10 in each mounting work of a TCP 7, and in the mounting method using this bonding tool 10, it is difficult to improve the work efficiency.
The reflow mounting method using a reflow oven is one of the mounting methods that permit high work efficiency by continuous work.
According to this reflow mounting method, the workpieces having their bonding pads smeared or plated with a solder in advance are continuously transferred to the reflow oven and as they go through the heating zone of the reflow oven, continuous bonding is performed.
However, the outer leads 6b of TCP 7 are formed of metal foil with a thin thickness about of 18 to 35 .mu.m.
Therefore, when the conventional reflow mounting method is applied to TCP 7 with such thin leads 6b, as shown in FIG. 4(a), the thin outer leads 6b are likely to be so deformed as to become separated from the bonding agent 11, and it occasionally happens that due to this deformation, the outer leads 6b are not bonded to the bonding areas 9 of the circuit board 8. Or, as shown in FIG. 4(b), a loose bonding will result from displacement caused by the deformation of the outer leads 6b.
There is a possibility that spoiled work occurs by a short-circuit to neighboring outer leads 6b, as shown in FIG. 4(c), due to displacement of the whole of the IC chip 5, which has light-weight outer leads 6b, caused by vibration or the like while the workpiece is being transferred to the reflow oven.
Furthermore, the leads 6b of TCP 7 are generally solder-plated or tin-plated to increase the wettability by solder for solder bonding. However, as the leads 6b of degrade in wettability with time, it has sometimes been difficult to have the top surface of the leads 6b sufficiently smeared with solder, making it impossible to obtain a required bonding strength.